1. Field of the Invention
The present invention generally relates to a film mode detecting apparatus and a method thereof, and more particularly, it relates to a film mode detecting apparatus for discriminating mode of an input image signal between film mode or non-film mode, and method thereof. The present application is based on Korean Patent Application No. 2001-74729, filed Nov. 28, 2001, which is incorporated herein by reference.
2. Description of the Prior Art
Generally, a film is made at the rate of 24 frames/second. In order to convert the rate of the film to the broadcasting standard of 60 fields/second of the National Television Standards Committee (NTSC), the rate of the picture source needs to be converted into a rate identical to that of the NTSC TV signal, which is 60 fields/second.
For showing film on a television, each sheet of film is scanned by a telecine. PAL or SECAM schemes scan twenty-five (25) frames/second, a rate which is not significantly different from the frame scanning rate of the film. Thus, PAL and SECAM formats pose no problem.
The NTSC scheme, however, scans signals at a rate of 60 fields/second, which is considerably different from the frame scanning rate of the film. Accordingly, for transmitting film for display on NTSC TVs, the screen speed must be adjusted to provide matching frame rates.
More specifically, the signals of 24 frames/second need to be converted into a rate of 60 fields/second, which means five (5) fields need to be generated from every two frames of the film. Accordingly, of two frames, three fields of the first frame are scanned, while two fields of the second frame are scanned by the 3:2 pulldown.
If the image signals are used with a film source and a non-film source mixed therein, in the process of interlace-to-progressive scanning conversion, 24 frames are increased to 30 frames by the characteristic of the 3:2 pulldown, and accordingly, 12 frames have image deterioration on the corresponding still images.
Further, in slow-motion play, there are unnatural pauses in the images. Another problem is that 24 frames of film source are stored at 60 fields, and thus storage capacity is wasted.
FIG. 1 is a block diagram showing a conventional film mode detecting apparatus.
As shown in FIG. 1, the film mode detecting apparatus includes a first buffer 100, a second buffer 101, a third buffer 102, an absolute value calculating unit 104, an adder 105, a limiter 106, a band-pass filter 107, a power calculating unit 108 and a mode detecting unit 109.
First, second and third buffers 100, 101, 102 store externally-inputted image signals with respect to each field. Differences between two different fields are obtained.
The absolute value calculating unit 104 calculates an absolute value of the pixel difference of the two fields.
The adder 105 adds up the absolute values calculated by the absolute value calculating unit 104. The adder 105 obtains median data of the sums of absolute differences of the pixels.
The limiter 106 removes values of the median data that exceed a predetermined threshold.
The band-pass filter 107 extracts signals at the period of 5.
The power calculating unit 108 calculates power of filtered signals. A large power value is calculated by the power calculating unit 108 with respect to the signals with the period of 5, while a value closer to ‘0’ is calculated with respect to the other signals.
The mode detecting unit 109 detects a mode of the inputted signals based on the calculated signal values. The mode detecting unit 109 compares the calculated power value of the signals with the predetermined threshold, and determines that the signals are from a film source when the power value exceeds the threshold, while determining that the signals are from a non-film source when the power value is under the threshold.
The conventional film mode detecting apparatus computes the SAD (sum of absolute differences) of two fields that are at a constant interval of 1/30 second, and detects the mode of the signal by using period of 5. The conventional film mode detection, however, loses its benefits when more noise is added disrupting the periodicity.
Further, in removing peaks which occur due to scene change, the limiter 106 excises values irrespective of degree of SAD. That is, the limiter 106 sometimes excises the values even when a relatively small SAD value is obtained. When this happens, accuracy of periodicity output deteriorates.
The mode detecting unit 109 pre-sets a threshold, and detects the mode of the signals by comparing the calculated power value with the preset threshold. As there can be variation in power value according to incoming streams, a fixed threshold is preset. When using the fixed threshold, an error can be generated in detecting the mode of signals.
Even though a threshold is set through a number of experiments, there still remains a high possibility of inaccuracy by the conventional film mode detection, as there are various types of incoming streams, and the slopes of noise and screen variations that occur due to, for example, fluctuation of the change of motion.